By David Tuller, DrPH
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In late August, I sent a letter to eClinicalMedicine, a Lancet journal, about an egregiously flawed paper called “Effects of therapeutic interventions on long COVID: a meta-analysis of randomized controlled trials.” The study was a mess. It concluded, with “high-certainty evidence,” that exercise training was effective and “should be prioritized.”
As I pointed out in my letter, some of the included studies did not even investigate people with Long COVID, and the majority of the research was found to be of low quality. So it was unclear why the investigators concluded that there was “high-quality” evidence of health benefits.
I never expect journals to behave appropriately. But earlier today, I received a response. As they informed me, they have contacted the authors to initiate a correction, although how robust that correction will be remains an open question.
They have also invited me to submit a politer version of my letter—a version without “accusatory or emotive phrasing” and with a “neutral and evidence-based tone.” Presumably that directive means removing words and phrases like “preposterous” and “cannot be taken seriously”—no matter how apt they might be, under the circumstances.
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Here’s the top of the letter I received from the journal:
“Dear Dr Tuller,
“Thank you for your notification regarding the issues identified in the published manuscript. We have contacted the authors of the article, and a corrigendum will be published to address these issues.
“If we proceed with considering your letter for publication, we kindly ask that you revise the language to align with scientific standards, avoiding accusatory or emotive phrasing. The tone should remain neutral and evidence-based.”
(The rest of the letter involved more detailed technical instructions for resubmitting a less “accusatory” missive.)
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And here is my revised version:
To the Editor:
A recent article, “Effects of therapeutic interventions on long COVID: a meta-analysis of randomized controlled trials,” reported “high-certainty evidence” that exercise training can improve health and “should be prioritized” [1]. However, this meta-analysis is flawed, rendering any such conclusions problematic.
First, the dozens of trials in the meta-analysis feature wildly divergent definitions of Long COVID. In some cases, it appears that trial participants did not even have Long COVID. As just one example, a Brazilian study included “subjects with coronavirus disease 2019 in the acute phase” [2]. Lumping together trials with extremely heterogeneous populations, including some without Long COVID, makes it challenging, if not impossible, to interpret the meta-analysis results.
Second, the authors themselves determined that the data used in the meta-analysis are of questionable value. They found that, according to Cochrane’s Risk of Bias Tool, only three of the included trials were at “low risk” of bias, with 33–the majority–at “high risk” of bias. Their analysis of quality of evidence for the many outcomes, per the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework [3], yielded similar results, with “27% of the evidence…rated as very low, 57% as low, 11% as moderate, and 5% as high.”
Given these acknowledged limitations, the confident assertion that exercise training is effective and “should be prioritized” is unwarranted, as is the statement that these findings constitute “high-certainty evidence.”
David Tuller
Center for Global Public Health
School of Public Health
University of California, Berkeley
1.Tan C, Meng J, Dai X, et al. Effects of therapeutic interventions on long COVID: a meta-analysis of randomized controlled trials. eClinicalMedicine. 2025;87:103412
2. Rodríguez-Blanco C, Bernal-Utrera C, Anarte-Lazo E, et al. Breathing exercises versus strength exercises through telerehabilitation in coronavirus disease 2019 patients in the acute phase: A randomized controlled trial. Clin Rehabil. 2022;Apr;36(4):486-497.
3. Guyatt GH, Oxman AD, Vist GE, et al. GRADE: an emerging consensus on rating quality of evidence and strength of recommendations. BMJ. 2008;336(7650):924-926.